Nanotechnology and engineered nanomaterials (ENM; particles less than 100 nanometers in one dimension) have firmly rooted themselves into nearly every aspect of daily life. As pharmaceutical and industrial advancements continue, human exposures to these new chemical sizes, shapes, and compounds are frequently introduced within the home, workplace, and as therapeutic drug-delivery platforms. Yet, the systemic health consequences of ENM exposures remain unclear. Specifically, multi-walled carbon nanotubes (MWCNT) have been robustly developed due to their highly desirable mechanical properties and substantial surface area as platforms of drug delivery and related industries; however these spear-like carbon compounds have been shown to imbed in the lower lungs after inhalation. While the pulmonary outcomes of traditional MWCNT exposure are currently under investigation; the cardiovascular effects and toxicities of these MWCNT have yet to be revealed and conclusions pertaining to non-traditional pharmacologic routes of exposure (ingestion, intravenous injection) have yet to be explored. Our laboratory has previously shown that systemic microvascular dysfunction follows after pulmonary titanium-dioxide nanoparticle exposure. However, not all nanoparticles should be considered identical, nor should their bioactivity or target tissues. Preliminary data related to this study evaluated the time-course and biomedical routes of MWCNT exposure, revealing significant sub-epicardial microvascular dysfunction stemming from gavage, inhalation, or co-incubation MWCNT exposure. The endothelium-dependent microvascular dysfunction of the coronary arterioles persists up to 168-hours after inhalation exposure. The present study proposes exposing rats to MWCNT via routes typically experienced in occupational and personal settings: inhalation, ingestion, or injection. Specific Aim 1 will establish the EC50 dosage, time- course, and MWCNT exposure route leading to the greatest sub-epicardial arteriolar dysfunction. Specific Aim 2 will evaluate the mechanisms leading to impairment of the coronary microcirculation due to MWCNT exposure. The working hypothesis of this application is that responses to acute MWCNT exposures will lead to significant coronary endothelium-dependent dysfunction due to alterations in NO bioavailability consistent with increased ROS scavenge; however these responses will be heavily dependent on the time course, dosage, and route of exposure. This study is innovative because it challenges the long-standing dogma that the lung is the primary target of ENM toxicity, or that the lung is necessary for biologic effects associated with ENM exposure. This study is forward thinking as it anticipates the inevitable non-pulmonary exposure routes in humans that will result from future ENM use. This study is significant because if the true therapeutic potential of nanotechnology is to be fully realized, its inherent toxicity must first b determined.